Isoindolequinones are known. Specifically, they are disclosed in U.S. Pat. No. 4,494,547 where they are generally defined according to the formula ##STR1## where R.sub.1 and R.sub.3 each separately is phenyl, substituted phenyl, alkyl of 1 to about 4 carbons, --CHO, --CH.sub.2 OR.sub.6, --CO.sub.2 R.sub.6, --COR.sub.6, hydrogen, or together with R.sub.2 is a divalent alkyl or alkenyl group of about 3 to about 5 carbons which form a cyclic ring; R.sub.2 is phenyl, substituted phenyl, --CH.sub.2 OR.sub.6, --CH.sub.2 CH.sub.2 OR.sub.6, alkyl of 1 to about 4 carbons, or with either R.sub.1 or R.sub.3 is a divalent alkyl or alkenyl group of about 3 to about 5 carbons which form a cyclic ring; R.sub.4 and R.sub.5, which may be the same or different each separately is hydrogen, alkyl of 1 to about 4 carbons, --OR.sub.6, --CO.sub.2 R.sub.6, --COR.sub.6, --CHO, --CH.sub.2 OR.sub.6 or together R.sub.4 and R.sub.5 is a buradiene group which forms a benzene ring; R.sub.6 is hydrogen or alkyl of 1 to about 4 carbons; provided that R.sub.1 and R.sub.3 are not both phenyl and that when R.sub.4 and R.sub.5 are both hydrogen, R.sub.1, R.sub.2 and R.sub.3 are not all methyl.
Such compounds are important radiosensitizers that sensitize hypoxic cells to the lethal effect of radiation in cancer radiotherapy. These compounds are also known to have antibiotic activity.
Isoindolequinones were first synthesized by the treatment of rhodium heterocycles, prepared from diketodiynes and Wilkinson's catalysts, with nitrosobenzene. Cycloadditions of oxazolium 5-oxides with 1,4-benzoquinones also give isoindole derivatives. The first report of naturally occurring isoindole-quinone, 2,5-dimethyl-6-methoxyisoindole-4,7-quinone, isolated from the sponge Reniera, has been synthesized in moderate yields to form a pyrrole derivative by the cycloaddition of a yield to a quinone. Zinc-induced intramolecular cyclizations of bis-(bromoacetyl)heteroaromatic compounds also give isoindolequinones.
The synthesis of these compounds, however, is often inefficient inasmuch as a multi-step reaction is often required. Furthermore, the use of solvents that are deleterious to the environment are also often required.
Therefore there is a need in the art for a more efficient and simplistic method for synthesizing isoindolequinones.